Bones of the Hand and Foot: Telling the Carpals and Tarsals Apart in a Spotter
Long bones are forgiving: a humerus looks like a humerus from across the room. The small bones of the wrist and ankle are not. In a spotter you get a single carpal or tarsal, often loose, and thirty seconds to name it. This guide gives one reliable feature for each bone, the standard mnemonics, and the applied anatomy that follows the identification question in the viva.
The carpal bones (8)
Two rows of four. From lateral (thumb side) to medial:
- Proximal row: scaphoid, lunate, triquetral, pisiform.
- Distal row: trapezium, trapezoid, capitate, hamate.
Mnemonic: She Looks Too Pretty, Try To Catch Her.
| Bone | How to recognise it |
|---|---|
| Scaphoid | Boat-shaped, the largest bone of the proximal row. Has a tubercle at its distal lateral end and a narrow waist in the middle. |
| Lunate | Crescent (half-moon) shaped; concave distally where it receives the head of the capitate. |
| Triquetral | Three-sided pyramid with a small oval facet on its palmar surface for the pisiform. |
| Pisiform | Small, pea-shaped, with only one articular facet (for the triquetral). It is a sesamoid bone in the tendon of flexor carpi ulnaris. |
| Trapezium | Saddle-shaped facet for the base of the first metacarpal; a groove on its palmar surface for the tendon of flexor carpi radialis. |
| Trapezoid | Small, wedge-shaped, broader dorsally than on the palmar side; articulates with the second metacarpal. |
| Capitate | The largest carpal, in the centre of the wrist. Its rounded head fits into the concavity formed by scaphoid and lunate. |
| Hamate | Wedge-shaped with a hook (hamulus) projecting from its palmar surface. |
Carpal applied anatomy worth memorising
- Scaphoid fracture: the commonest carpal fracture, typically across the waist after a fall on the outstretched hand. The blood supply enters mainly through the distal part, so the proximal fragment is at risk of avascular necrosis. Tenderness in the anatomical snuff box is the classical sign.
- Lunate dislocation: the lunate is the carpal most often dislocated, usually anteriorly, where it can press on the median nerve.
- The flexor retinaculum attaches laterally to the tubercle of the scaphoid and the ridge of the trapezium, and medially to the pisiform and the hook of the hamate. These four points bound the carpal tunnel; compression of the median nerve here is carpal tunnel syndrome.
- The ulnar nerve and artery pass superficial to the retinaculum, lateral to the pisiform, in the canal of Guyon.
Metacarpals and phalanges
- Five metacarpals. The first is the shortest and stoutest and articulates with the trapezium by a saddle joint. The second is the longest. The third carries a styloid process at the dorsolateral side of its base.
- Fourteen phalanges: three in each finger, two in the thumb.
The tarsal bones (7)
Talus, calcaneus, navicular, cuboid, and the medial, intermediate and lateral cuneiforms. Mnemonic: Tiger Cubs Need MILC (talus, calcaneus, navicular, medial, intermediate, lateral cuneiform, cuboid).
| Bone | How to recognise it |
|---|---|
| Talus | Has a head, neck and body. The body carries a pulley-shaped upper surface (the trochlea) for the tibia. No muscle is attached to the talus; most of its surface is articular. |
| Calcaneus | The largest tarsal. A large posterior tuberosity (heel) and a shelf on the medial side, the sustentaculum tali, which supports the head of the talus. A groove for the tendon of flexor hallucis longus runs beneath the sustentaculum. |
| Navicular | Boat-shaped, with a concave proximal facet for the head of the talus and a tuberosity on the medial side for tibialis posterior. |
| Cuboid | Cube-like, on the lateral side of the foot. Its plantar surface has a groove for the tendon of peroneus longus. |
| Medial cuneiform | The largest cuneiform; articulates with the first metatarsal. |
| Intermediate cuneiform | The smallest; wedge with the base dorsally, articulates with the second metatarsal. |
| Lateral cuneiform | Articulates with the cuboid laterally and the third metatarsal distally. |
Side determination of the two bones that get asked
Calcaneus: hold it with the large tuberosity pointing backwards and the articular facets for the talus facing upwards. The sustentaculum tali projects to the medial side, so it points to the side the bone belongs to. The peroneal (fibular) trochlea is on the lateral surface.
Talus: hold it with the trochlea facing upwards and the head pointing forwards. The trochlea is wider in front than behind; the medial side of the body carries a small comma-shaped facet for the medial malleolus, while the lateral side has a large triangular facet for the lateral malleolus. The head points forwards and slightly medially.
Tarsal applied anatomy
- Fracture of the neck of the talus can cut off the blood supply to the body, which lies behind the fracture, causing avascular necrosis.
- The calcaneus is the tarsal most often fractured, classically after a fall from a height onto the heels; the same injury can fracture the vertebral column, so examine the spine as well.
- The head of the talus is supported below by the plantar calcaneonavicular (spring) ligament, which runs from the sustentaculum tali to the navicular. Weakness of this support contributes to flat foot.
- The tuberosity of the fifth metatarsal gives attachment to peroneus brevis and can be avulsed in an inversion injury.
- The arches of the foot: the medial longitudinal arch is formed by calcaneus, talus, navicular, three cuneiforms and the medial three metatarsals; the lateral longitudinal arch by calcaneus, cuboid and the lateral two metatarsals.
Metatarsals and phalanges of the foot
- Five metatarsals. The first is the shortest and thickest; the second is the longest. The fifth has a prominent tuberosity at its base.
- Fourteen phalanges, with two in the great toe and three in each of the others, as in the hand.
Practice method for spotters
Lay out the carpals or tarsals of one side from your bone set and assemble them into their anatomical position on the table. Then mix them, pick one at random and name it in under ten seconds using the single feature above. Afterwards, check each bone's articulations in 3D in the Anatomy Lab.
This is a revision aid prepared by XBONZ for first-year medical students. Follow your university syllabus and your department's recommended textbooks for examination purposes.